PEX 8664, PCI Express Gen 2 Switch, 64 Lanes, 16 Ports

© PLX Technology, www.plxtech.com

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5/14/2009, Version 1.1

performancePAK

TM

Exclusive to PLX, performancePAK is a suite of unique

and innovative performance features which allows

PLX’s Gen 2 switches to be the highest performing Gen

2 switches in the market today. The performancePAK

features consists of the Read Pacing, Multicast, and

Dynamic Buffer Pool.

Read Pacing

The Read Pacing feature allows users to throttle the

amount of read requests being made by downstream

devices. When a downstream device requests several

long reads back-to-back, the Root Complex gets tied up

in serving that downstream port. If that port has a narrow

link and is therefore slow in receiving these read packets

from the Root Complex, then other downstream ports

may become starved – thus, impacting performance. The

Read Pacing feature enhances performances by allowing

for the adequate servicing of all downstream devices.

Multicast

The Multicast feature enables the copying of data

(packets) from one ingress port to multiple (up to 15)

egress ports in one transaction allowing for higher

performance in dual-graphics, storage, security, and

redundant applications, among others. Multicast relieves

the CPU from having to conduct multiple redundant

transactions, resulting in higher system performance.

Dynamic Buffer Pool

The PEX 8664 employs a dynamic buffer pool for Flow

Control (FC) management. As opposed to a static buffer

scheme which assigns fixed, static buffers to each port,

PLX’s dynamic buffer allocation scheme utilizes a

common pool of FC Credits which are shared by other

ports. This shared buffer pool is fully programmable by

the user, so FC credits can be allocated among the ports

as needed. Not only does this prevent wasted buffers and

inappropriate buffer assignments, any unallocated

buffers remain in the common buffer pool and can then

be used for faster FC credit updates.

visionPAK

TM

Another PLX exclusive, visionPAK is a debug

diagnostics suite of integrated hardware and software

instruments that users can use to help bring their systems

to market faster. visionPAK features consist of

Performance Monitoring, SerDes Eye Capture, Error

Injection, SerDes Loopback, and more.

Performance Monitoring

The PEX 8664’s real time performance monitoring

allows users to literally “see” ingress and egress

performance on each port as traffic passes through the

switch using PLX’s Software Development Kit (SDK).

The monitoring is completely passive and therefore has

no affect on overall system performance. Internal

counters provide extensive granularity down to traffic &

packet type and even allows for the filtering of traffic

(i.e. count only Memory Writes).

SerDes Eye Capture

Users can evaluate their system’s signal integrity at the

physical layer using the PEX 8664’s SerDes Eye

Capture feature. Using PLX’s SDK, users can view the

receiver eye of any lane on the switch. Users can then

modify SerDes settings and see the impact on the

receiver eye. Figure 5 shows a screenshot of the SerDes

Eye Capture feature in the SDK.

Figure 5. SerDes Eye Capture

Error Injection & SerDes Loopback

Using the PEX 8664’s Error Injection feature, users can

inject malformed packets and/or fatal errors into their

system and evaluate a system’s ability to detect and

recover from such errors. The PEX 8664 also supports

Internal Tx, External Tx, Recovered Clock, and

Recovered Data Loopback modes.

Applications

Suitable for host-centric as well as peer-to-peer traffic

patterns, the PEX 8664 can be configured for a wide

variety of form factors and applications.

Host Centric Fan-out

The PEX 8664, with its symmetric or asymmetric lane

configuration capability, allows user-specific tuning to a

variety of host-centric applications. Figure 6 shows a